Adhesive composition



Patented Dec. 15, 1936 I UNITED STATES PATENT OFFICE ADHESIVECOMPOSITION Donald E. Edgar, New Brunswick, N. 3., assignor to E. I. duPont de Nemours & Company, Wilmington, Del., a corporation 'of DelawareNo Drawing.

Application February 23, 1933,

Serial No. 658,270

6 Claims.

ing a suitable bond. A further object is to provide an adhesivecomposition which does not require high temperatures to securethermo-hardening to give a suitable bond and which is not dependent onany chemical change for the attainment of such bond.

A further object is to provide heat energizable adhesives which arehighly resistant to water, thereby affording a substantially waterproofjoint.

A still further object is to provide a heat energizable adhesive whichis of good color so that its utility in conjunction with light coloredor transparent materials is not precluded. A further object is toprovide such an adhesive which is initially and permanently flexible andis substantially inert so that it is not appreciably affected by normaltemperatures or exposure to the air.

Another object is to provide a heat energizable adhesive which will givea bond not softening under conditions of normal or slightly elevatedtemperatures, so that slippage of the cemented surfaces does not takeplace. v

A still further object is the provision of a heat en'ergiiable cementwhich is sufficiently elastic thermoplastic synthetic resin with acellulose nitrate in a heat energizable adhesive. A preferred form ofthe adhesive of the present invention comprises a cellulose nitratehaving a nitrogen content of 10.0 to 12.2% and a polyhydricalcoholpolybasic acid synthetic resin modified by an agent from thegroup consisting of vegetable drying and semiand non-drying oils,stearic acid, oleic acid, and higher alcohols such as butyl, and amylalcohol, et cetera, dispersed in a suitable solvent mixture.

The following examples are given to illustrate the invention:

Example 1 Per cent Cellulose nitrate (approximately 4 sec. vis- Theviscosities given throughout this specification are measured inaccordance with method outlined in A. S. T. M. tentative specificationsand tests for soluble nitrocellulose, designation D301-T. The nitrogencontent of the cellulose nitrate in the above examples was 11.8 to12.15%.

The two above formulas are quite similar except for the ultimateviscosity of the adhesive,

the first having approximately twice the viscosity 40 of the second.

*The synthetic resin in the above examples is a reaction product 01:-

The resin was compounded by charging the above ingredients into analuminum kettle fitted with a mechanical stirring device and athermometer. The batch was heated up to 225 C. in thirty minutes andheld at this temperature until an acid number of 13-15 was reached,stirring being maintained throughout the run. The heating cycle tookabout 4 hours.

Example 3 Per cent Cellulose nitrate (approximately 2 sec. viscosity)-8. 2 Denatured alcohol 10.0 Toluol- 33.0 Ethyl acetate 219.0 Dibutylphthalate 6.4 'Synthetic resin 13.4

This example represents a slight modification Per cent Phthalicanhydride 40.5 Stearic acid 35.4 Glycerine 24.1

The resin was prepared as described in Exampie 1.

Emmple 4 Per cent Cellulose nitrate 10.0 Tricresyl phosphate 3.0 Ethylaceta 15.0

Toluol 22.0 Denatured alcohol 30.0 Synthetic resin 20.0

' The synthetic resin in this formula was the reaction product of:-

Per cent Phthalic anhydride 54.3

- Gly r 24.2 Castor oil 221.5

This resin was prepared by charging all of the ingredients into a kettleand heating to 200 C. in 1 hours. This temperature was maintained forapproximately two hours or until an acid number of 73-77 was reached.

Example 5 Per cent Cellulose nitrate 10 Ethyl acetate 20 Toluol 30Denatured ethyl alcohol 28 "Synthetic" resin 12 The "synthetic" resin inthis example was the reaction product of:-

' Per cent Diethylene glycol 41.7 Phthalic anhydrlde 58.3

The resin was prepared by charging the materials into a kettle andheating to 240-250 C. and maintaining this temperature until an acidnumher under 40 was obtained. This required slightly under four hours toaccomplish.

The cellulose nitrate used in the above two examples (Examples 4 and 5)had a nitrogen content of approximately 10.6%.

Example 6 Per cent Cellulose nitrate (nitrogen 11.4 to 11.6%) 9.9Denatured ethyl alcohol 5.8 Ethyl acetate 40.0 Toluol- 32.6 Acetone 1.2Dibutyl phthalate 4.4 *Synthetid resin 6.1

.The "synthetic resin in this formula was the reaction product of:-

Per cent Diethylene glycol 37.4 Phthalic anhydride 47.6 Stearic acid15.0

The resin was prepared by charging the materials into a kettle andheating to -200 C. This temperature was maintained for approximately 4hours, at the end of which time the acid number was 40-50.

Example 7 Per cent Cellulose nitrate (nitrogen 11.4 to 11.6%) 10.0Denatured alcohol 6.0 Ethyl acetate 37.0 Toluol 32.5 Dibutyl phthalate4.5 Synthetic resin 10.0

*The synthetic resin in this example is the same as that used in Example6.

Example 8 Per cent Cellulose nitrate (80 sec. viscosity) 11.3 Denaturedalcohol 8.6 Dibutyl phthalate 13.5 Toluene 16.0 Ethyl acetate 19.0Synthetic -resin 30.7'

The nitrogen content of the cellulose nitrate in this example is11.4-11.6% and the synthetic resin is the same as used in Example 6.This composition is particularly suited for coating on fabrics and otherporous surfaces because of its relatively high viscosity which preventsundesirable impregnation.

Example 9 Per cent Cellulose nitrate sec. viscosity) 15, 0 Denaturedalcohol 15. 0 Ethyl acetate 31.0 Dibutyl phthalate 8.0 Toluol 15.0Synthetic resin 16. 0

The synthetic resin in this formula is atoluene-sulfonamide-formaldehyde condensation product. The adhesivedried to practically a tack-free stage before joining the surfaces andyet, when subjected to normal heat and pressure in joining the surfaces,provided a very satisfactory bond.

The compounding of the adhesive composition in all of the above exampleswas carried out substantially as follows: The non-solvents, such astoluol, were first added to wet the cellulose nitrate in order tofacilitate its solution when the active solvents were added later. Theactive solvents, such as ethyl acetate, and the solvent softeners, suchas dibutyl phthalate, were then added and the mixture agitated untilcomplete solution was obtained. Finally, the resin constituent alreadydissolved in a portion of the active solvent of the ultimate formula wasadded and the mixing continued until homogeneity was secured. Theadhesive composition was then ready for use. The adhesives described inthe above examples are substantially transparent and colorless. It willbe understood that these compositions may be colored by theincorporation of a suitable coloring agent, such as a dye or a pigment,or rendered opaque by the addition of a suitable filler, by processeswell known in the art of preparing colored and opaque lacquers.

The above examples are given merely to illustrate specific embodimentsof the invention which, in its broader phases, contemplates a heatenergizable adhesive comprising a synthetic resin and a cellulosenitrate having a nitrogen content of 10.0 to 12.2%.

The viscosity characteristic of the cellulose nitrate is not critical solong as the nitrogen content is kept within the specified limits.Cellulose nitrate having a viscosity of below 4 seconds can be usedsatisfactorily and the upper limit of the viscosity characteristic is ony dependent upon the workability of the solution for practical purposes.For application of the adhesive to a non-porous surface, such as metal,glass, regenerated cellulose sheets, and the like, a low viscositycellulose nitrate is. satisfactory, while for a porous surface, such asfabric and certain papers, a high viscosity cellulose nitrate is more tobe desired. Cel ulose nitrate having a viscosity of seconds has beenfound very satisfactory for general application.

The type of polyhydric alcohol-polybasic acid synthetic resin operativein the preferred form of the present invention can be varied withoutlimit, although certain types of polyhydric alcohol-polybasic acidsynthetic resins are much more suitable than others. A resin having theproperty of being a solvent for cellulose nitrate and having a highcoefficient of plasticity, that is, considerable increase in mobilityper degree rise in temperature is most suitable. The resins modifiedwith non-drying oils have been found especially advantageous. Cocoanut,cottonseed, hy-

drogenated cottonseed, and castor oils may be mentioned as non-dryingoils of particular merit.

Higher aliphatic acids, such as oleic, and stearic, are also verysuitable as modifyin agents, but it is not preferred to use these acidsin amounts greater than 50% by weight of the resin. Butyl alcohol is anoutstanding alcohol modifying agent, but other high boiling alcohols.such as hexyl, propyl, amyl, and benzyl alcohols, cyclohexanol andterpineol are also useful. Resins modified with rosin or gums, such askauri, copal, and the like, may be used but they are not as desirable asresins modified with the above disclosed agents.

As is well known in the art, the polyhydric alcohol-polybasic acidsynthetic resins may be made from a wide variety of polyhydric alcoholsand polybasic acids. Dl-hydric and tri-hydric alcohols, thoughpreferred, need. not necessarily be used, as the higher polyhydriccompounds, such as sorbitol, pentaerythritol, and the like,

may also be used. Polyhydric ether alcohols,

erol, et cetera, are particularly advantageous because of the highcompatibility and high coemcient of plasticity characteristic of resinsmade therefrom. In place of phthalic acid many other acids, such asmalic, adipic, succinic, trimellitic, dilactylic, fumaric, and sebacioacids can be used in the manufacture of these resins.

Other resins having solvent power for cellulose nitrate and having highcoefficients of plasticity, for example, aryl sulfonamide formaldehyderesins, such as the toluenesulfonamide-formaldehyde resin used in thecomposition of Example 9, xylenesulfonamide-formaldehyde resins,benzenesulfonamide-formaldehyde resins, et cetera, may be used. Otherresins such as vinyl acetate resins, vinyl acetate-vinyl chlorideresins, and certain phenol-formaldehyde resins and urea formaldehyderesins may be used. The toluenesulfonamide resins and the polyhydricalcoholpolybasic acid resins are preferred because of theircompatibility and high coefficient of plasticity. Certain types of thislatter class of resins, i. e., polyhydric alcohol-polybasic acid resins,modified with high molecular weight acids and/or higher molecular weightalcohols, or those from dihydric alcohols, particularly ether alcoholspreferably with high molecular weight acids, represent the mostpreferred embodiment of the present invention because of their embodyingthe advantageous characteristics of freedomv from stickiness, highcoefficient of plasticity, high degree of heat energizability, highercapacity of being resoftened by high temperatures before losing theirheat energizability. high compatibility with cellulose nitrate, highwater resistance, and excellent strength of bond.

As shown in the examples. the proportion of cellulose nitrate tosynthetic resin can be varied widely. depending upon the specificproperties desired. A range of 0.6-2.0 parts of synthetic resin to onepart of cellulose nitrate is preferred, but highly useful adhesivecompositions may be employed with from 2-5 parts of resin to one part ofcellulose nitrate. It is necessary in order to provide a satisfactoryadhesive composition that the synthetic resin be compatible w'th thecellulose nitrate, that is, the synthetic resin must not separate fromthe cellulose nitrate when deposited in a film but give a homogeneouscoating.

As shown in the above examples, the use of a plasticizer in theseadhesive compositions is optional and dependent, to a considerabledegree, upon what properties are desired in the adhesive and the type ofsynthetic resin employed. For example, if the adhesive compositioncontains cellulose nitrate and, as a synthetic resin, diethylene glycolphthalate, or other polybasic acid ester of a dihydric ether alcohol, noplasticizer is necessary, since these resins are of the soft, lowmelting type and suflicient heat energizability is developed throughthis medium, but in other cases where the synthetic resin is of theharder type, the addition of plasticizer is preferred in order to obtainsuflicient heat energizability to provide satisfactory bondingproperties at suitable temperatures. When a plasticizer is used, itshould be selected from the socalled "solvent type, that is, a solventfor cellulose nitrate. Such plasticizers as dibutyl phthalate, dibutyltartrate, tricresyl phosphate, triacetin, and ethyl meta-sulfonamide aresuitable.

With respect to the solvent mixtures employed in these compositions,their function is simply to provide a suitable vehicle for the filmforming ingredients in order that a satisfactory film may be laid andthey do not affect the operation of the composition after the film hasdried out. The solvents and solvent mixtures which may be employed willreadily occur to those skilled sive will set up quickly and will developa strong in the art. The proportions of ingredients in the solventmixture and the proportion of solvent to film forming ingredients inthese compositions may be varied almost without limit, depending ontheparticular properties of the adhesive composition desired, as will beunderstood by those skilled in the art.

The adhesive compositions of the present invention are practicallyidentical with ordinary cellulose nitrate lacquers in appearance and canbe applied to objects which are to be cemented together in exactlythesame manner as clear lacquers are applied, namely, by brushing, dipping,spraying, or roller coating methods. The adhesive compositions are lightin color and deposit a clear, nearly colorless film. After applying theadhesive to the objects which are to be joined together, the adhesivefilm is allowed to dry, which operation usually takes from 3-20 m nutesat room temperature, depending somewhat on the type of material coatedand the particular composition of the adhesive. Force drying. of course,may be employed. When the solvents of the composition have completelyevaporated, the objects to be cemented together are brought intointimate contact with each other and heated with a heat press, roll, orfiat iron. An ordinary electric flat iron may be used. A temperature ofl30-150 C. is suitable and little pressure is necessary, 2 to 15 poundsper square inch being suflicient, although it will be apparent thatgreater pressure is desirable. The exact heating time is largelydependent on the conductivity of the material through which the heatmust pass to melt the adhesive, but in cementing most materials the heatneed be applied only momentarily. On cooling, the adhebond between theobjects cemented together.

By employing pressures of 10,000 pounds per square inch these adhesivecompositions will give a good bond without supplying heat from anyexternal source. although ordinarily it is more convenient to employlight pressure and heat.

The adhesive compositions of the present invention. and particularlythose employing polyhydric alcohol-polybasic acid resins, deposit filmswhich are characterized by a considerable degree of elasticity,excellent initial and retained flexibility and adhesion and have verylittle color, odor, or taste. Furthermore, the bond is'waterproof and,unlike rubber adhesives, the ad'- hesive films are, in general, notsusceptible to oxidation and are, therefore, of greatly improveddurability over films deposited from the known rubber adhesives. Sincethese adhesive compositions do not depend upon evaporation of solvent toset up, they can be used to advantage between impervious surfaces. Aparticular advantage of these adhesives lies in the fact that when usedwith relatively light weight materials, such as paper, cardboard,regenerated cellulose sheets, and the like, they do not cause warping,curling, or staining.

The heat energizable compositions of the present invention areapparently substantially unchanged chemically upon heating togi-ve abond, since a bond of exceptional strength may be secured by a momentaryapplication of heat in most instances. It is believed that the resincomponent of the adhesive is substantially unaffected by the heat,except where prolonged or a very high temperature is employed, and thatpractically no polymerization occurs. This is borne out by the fact thatthe adhesive film may be again softened, at least once, after the bondhas been effected by further application of heat. This critical point ofsoftening is, however, sufficiently far above normal temperatures sothat there is an ample safety factor against possible loosening orslipping of the bond at normal temperatures.

Another advantage of the adhesive compositions of the present inventionis that they give films of such flexibility and elasticity that theyallow the embossing of bonded materials such as paper, fabrics, leather,and the like, without destruction of the bond. These properties also areof distinct advantage where two surfaces of dissimilar coefiicients oflinear expansion are joined, a successful bond for this purpose beingdependcut on a slight amount of elasticity or cold fiow. Also materialscoated with the adhesives of the present invention may be stored forextended periods without danger of sticking together and ,without lossof adhesive qualities, so that they may be united at any desired timeupon the application of heat and pressure.

While there are many uses for the adhesives herein described, which willreadily occur to those skilled in the art, a partial list of uses forwhich these adhesives have been found particularly adapted is givenbelow:

1. Regenerated cellulose sheets (plain or moisture proofed) to fabric,paper, cardboard, metal foil, regenerated cellulose sheets, leather,tissue paper, and cellulose ester films;

' 2. Fabric to fabric, paper, cellulose ester films, fiber board, metalfoil, and lacquered or rubberized fabric;

3. Metal foil to metal foil, wood, paper, cardboard, glass, and tissuepaper;

- 4. Veneer to wood and fiber board;

5. Glass to glass and cellulose ester films.

The adhesives of the present invention are particularly useful incementing aluminum foil to various impermeable surfaces for the following practical purposes:

1. For coating the inside of various types of tanks in order to makethem more resistant to the solution stored in the tank:

2. For coating the outside of petroleum field tanks and various othertanks in order to obtain the maximum reflection of heat and henceminimum evaporation losses, as well as to supply a durable coating,particularly resistant to corrosion by sulfur gases;

3. For coating pipe lines, particularly buried pipe lines;

4. For coating cables, particularly underground cables;

5. For obtaining a durable, minimum air resistant coating for fabricused on aeroplane wings and fuselage;

6. For obtaining a durable coating with minimum air resistance on theexterior of dirigibles;

7. For coating both the inside and outside of refrigerators 8. For useas a substitute for gold-heaters skin, and other uses where a veryimpermeable, light weight, flexible material is necessary;

9. For coating wood shingles in order to make them more durable.

These adhesives are also particularly useful for impregnating paper,fabric, and similar materials -llCh are subsequently used between twosurfaces which are to be united. The employment of these adhesives forcementing surfaces impermeable to the passage of solvent vapors, such asmetal to metal, moisture proof regenerated cellulose sheeting tomoisture proof regenerated cellulose sheeting, and the like, is 'veryadvantageous due to the fact that the setting up of the presentadhesives isnot dependent upon evapora- Hon of solvents. It will beapparent to those skilled in the art that most adhesives cannot be usedfor such purposes, as they depend upon solvent evaporation. Also, theseadhesives are of particular advantage in cementing celluloid, cel--lulose acetate silk, and the like, to metal or other surfaces, becausethe adhesive can be applied to the metal only, then on drying, thecelluloid, cellulose acetate silk, etc., can be united to the metal byheat and pressure without being brought into contact with the solventsin the adhesive, which would deleteriously affect the celluloid, etcetera.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A heat energizable cement comprising as essential ingredientsnitrocellulose, a synthetic resin having a high coefficient ofplasticity, and at least one solvent, said resin being present in suchproportion that a film of the said cement when dry is substantiallynon-tacky at ordinary temperatures, is adhesive under a pressure of lbs.to 10,000 lbs. per sq. in. at ordinary temperatures, is soft within therange of C. to C. and is adhesive under a pressure of 2 lbs. to 15 lbs.per sq. in. within the range of 130 to 150 C.

2. Product of claim 1 in which the resin is of the polyhydricalcohol-polybasic acid type.

3. Product of claim 1 in which the resin is of the arylsulphonamide-formaldehyde type.

4. Product of claim 1 in which the resin is a vinyl polymer,

5. A composition of matter having approximately the following formula:

Percent by weight Cellulose nitrate (approx. 4 sec. viscosity) 8.2Denatured alcohol 10.0 Toluol 29.0 Dibutyl phthalate 6.4 Ethyl acetate33.0

Synthetic resin (castor oil modified reaction product of glycerol andphthalic anhydlide) 13.4

6. Product of claim 1 having the following composition:

Per cent Cellulose nitrate 8.2 Alcohol 10.0 Diluent 29.0 Active solvent33.0 Solvent plasticizer 6.4 Thermoplastic synthetic resin 13.4

DONALD E. EDGAR.

